The present invention relates to magnetic domain wall shift register memory devices, and more specifically, to magnetic domain wall shift register memory devices with high magnetoresistance ratio structures and methods of fabricating the same.
Magnetic domain wall shift register memory devices require sensing elements to read out the signal from the magnetic track. Currently, there are two major types of sensing elements that are implemented. One sensing type is a conductive wire that directly contacts with the track and reads the signal by an anomalous Hall Effect. Another sensing type is a magnetic tunnel junction (MTJ) disposed on top or at the bottom of the track, and reads the tunnel magnetoresistance (TMR). The signal from the anomalous Hall Effect is much smaller than that from MTJ. As such, the MTJ is a promising sensing element for reading out the signal from the magnetic track. As the MTJ is applied as a reader, the TMR ratio is a key factor in reading the signal. The TMR ratio of the MTJ is usually low when permalloy is used as the magnetic track. One can increase the TMR by thickening an MgO (magnesium oxide) layer, but the magnetoresistance dramatically increases. As such, a higher voltage for the same reading current is required, and generally is unsuitable for real time readings.